Synthesis and Characterization of Ruthenium(II) Complexes Containing Chiral Bis(ferrocenyl)−P₃or −P₂S Ligands. Asymmetric Transfer Hydrogenation of Acetophenone

Abstract

A number of new chiral bis(ferrocenyl)−triphosphine ligands have been synthesized by the reaction of cyclohexylphosphine with different chiral ferrocenyl aminophosphines in hot acetic acid. The thioether ligand bis{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl} sulfide has been similarly prepared by the reaction of (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl acetate with either (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl mercaptan or (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl mercaptan sodium salt. All the above reactions proceed with retention of configuration on the side-chain stereocenters of the starting materials. Monomeric Ru(II) complexes containing either chloride or acetonitrile coligands have been prepared with all the chiral tridentate ligands. Both the new ligands and the ruthenium complexes have been characterized by multinuclear NMR spectroscopy. The structure of [(S)-(R)-Pigiphos]RuCl2·2CH2Cl2 ((S)-(R)-Pigiphos = bis{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphosphine) has been determined by X-ray diffraction. The asymmetric transfer hydrogenation of acetophenone catalyzed by various Ru(II) bis(ferrocenyl) tridentate complexes in propan-2-ol is also reported.

Synthesis and Reactivity of Ru-, Os-, Rh-, and Ir-Halide−Sulfoxide Complexes

“…230 The mononuclear nature of fac-RuCl 2 (ttp), as opposed to the triply chloro-bridged bimetallic structure of [(etp)Ru-(µ-Cl) 3 Ru(etp)]Cl, was attributed to purely steric reasons, as the Ru(ttp) unit occupies a larger volume than Ru(etp). 230 Similar five-coordinate mononuclear complexes of formula RuCl 2 (P 3 ) were obtained from 8 with chiral bis(ferrocenyl)-triphosphine ligands such as (S)-(R)-Pigiphos (bis{(S)-1-(R)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphosphine, Chart 18), 234 with the chiral ligand (R)-Ph 2 PCH 2 CH-(PPh 2 )CH 2 CH 2 PPh 2 (etp*), 235 with PhP(CH 2 CH 2 CH 2 P-(C 6 H 11 ) 2 ) 2 (Cyttp), 236 and with the tridentate phosphinite ligand MeC(CH 2 OPPh 2 ) 3 (triphox, Chart 18); 212 interestingly, this latter complex showed a triply chloro-bridged dimeric structure in the solid state, while in chloroform solution a significant part of the complex existed as the monomeric form.…”

Polydentate phosphines

“…19) a cobalt complex was synthesized and analyzed [{(CH 3 ) 2 CHCH 2 CH 2 C(CH 2 PPh 2 ) 3 }Co {O(O)CCH 3 }]BF 4 [62].…”

(2Sp,4R,8Sp)-4-Methyl-1-phenyl-diferroceno-5-Z-ethylene-1-phosphinoxide

“…For instance, Barbaro et al used diferrocenyl phosphorous ligands for Ru(II)-catalyzed hydride transfer to the small molecule acetophenone and observed 72% e.e. at a conversion rate of 99% [4]. The e.e.…”